Defoaming agent and associated methods of use

ABSTRACT

Defoaming agents comprising a silicone oil and silica particulates, lubricating oil compositions comprising the defoaming agent, methods of lubrication using a lubricating oil composition comprising the defoaming agent, and methods of reducing the foaming tendency/stability and/or improving the air release rates of non-aqueous fluids, such as lubricant oils, are provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/007,087, filed on Jun. 3, 2014, which is incorporated herein by reference.

BACKGROUND

Lubricating oils, including hydraulic oils and crankcase oils, are often used to reduce friction between members and to assist in the operation of many mechanical constituents. Commonly, such lubricating oils are used in environments in which the oil is subject to mechanical agitation in the presence of air. As a consequence, air may undesirably become entrained in the oil and/or cause the formation of foam.

Foam generally refers to a collection of air bubbles formed in or on the surface of a liquid, while air entrainment generally refers to the dispersion of air bubbles within a liquid. Air entrainment and foaming in lubricating oils can be a serious concern as it may lead to problems such as inadequate lubrication, fluctuation of hydraulic pressure, poor hydraulic system performance, incomplete oil films, component wear due to reduced lubricant viscosity, and fluid deterioration due to accelerated oxidation, which may eventually lead to mechanical failure or the like. Lubricating oils therefore usually contain a defoaming agent.

In general, as a defoaming agent for lubricating oil, it is known to employ a silicone-based defoaming agent, such as polydimethylsiloxane (PDMS), fluorosilicones and silicone glycols. For instance, U.S. Pat. No. 6,251,840 discloses lubricating fluids comprising a silicone-based antifoam agent. Similarly, U.S. 2014/0018267 discloses a lubricating fluid comprising a combination of three polydimethylsiloxane antifoam agents.

SUMMARY

The present disclosure generally relates to a defoaming agent comprising a silicone oil and silica particulates, lubricating oil compositions comprising the defoaming agent, methods of lubrication using a lubricating oil composition comprising the defoaming agent, and methods of reducing the foaming tendency and/or improving the air release rates of non-aqueous fluids, such as lubricant oils.

Accordingly, in one embodiment, a lubricating oil composition is provided that comprises: (i) a base oil; and (ii) a defoaming agent comprising (a) a silicone oil and (b) silica particulates.

In another embodiment, the present disclosure provides a method of applying a lubricating oil composition to a surface in relative movement to another surface, wherein the lubricating oil composition comprises: (i) a base oil; and (ii) a defoaming agent comprising (a) a silicone oil and (b) silica particulates.

In yet another embodiment, the present disclosure provides a method of decreasing the foaming tendency of a non-aqueous fluid, the method comprising: providing a non-aqueous fluid having a first foaming tendency as measured according to ASTM D892; and adding a defoaming agent comprising a silicone oil and silica particulates to the non-aqueous fluid so as to reduce the first foaming tendency to a second foaming tendency.

In yet another embodiment, the present disclosure provides a method of improving the air release rate of a non-aqueous fluid, the method comprising: providing a non-aqueous fluid having a first air release rate as measured according to ASTM D3427; and adding a defoaming agent comprising a silicone oil and silica particulates to the non-aqueous fluid so as to increase the first air release rate to a second air release rate by reducing the air release time.

The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

DETAILED DESCRIPTION

Lubricating oil compositions of the present disclosure generally comprise a base oil and a defoaming agent that comprises a silicone oil and silica particulates.

A. Base Oil

The base oil may comprise one or more mineral oils, one or more synthetic oils, or a mixture of one or more mineral oils and one or more synthetic oils; thus, as used herein, the term “base oil” may refer to a mixture containing more than one base oil. There are no particular limitations regarding the base oil, and various conventional mineral oils, synthetic oils, as well Group I-III mineral base oils, Group IV poly-alpha olefins (PAOs), Group II-III Fischer-Tropsch derived base oils, Group V base oils, and mixtures thereof may be used.

By “Group I”, “Group II” “Group III” and “Group IV” and “Group V” base oils, it is meant base oils according to the definitions of American Petroleum Institute (API) for categories I, II, III, IV and V. These API categories are defined in API Publication 1509, 15th Edition, Appendix E, April 2002.

Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (“VI”) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which color and color stability are important, and VI and oxidation stability are of secondary importance.

Paraffinic base oils have higher VI (generally >95) and a high pour point. Such base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important.

Synthetic oils include hydrocarbon oils and halosubstituted hydrocarbon oils, such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), Fischer-Tropsch derived base oils, alkyl naphthalenes and dewaxed waxy isomerates. Synthetic hydrocarbon base oils sold by the Royal Dutch/Shell Group of Companies under the designation “XHVI” (trade mark) may be conveniently used.

Fischer-Tropsch derived base oils may be used as the base oil. By the term “Fischer-Tropsch derived” is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Suitable poly-alpha olefin base oils that may be used include those derived from linear C₂ to C₃₂, preferably C₆ to C₁₆, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and 1-tetradecene.

Preferably, the base oil comprises mineral oils and/or synthetic oils which contain more than 80% wt of saturates, preferably more than 90% wt., as measured according to ASTM D2007.

It is further preferred that the base oil contains less than 1.0 wt. %, preferably less than 0.03 wt. % of sulfur, calculated as elemental sulfur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 or ASTM D3120.

Preferably, the viscosity index of the base oil is more than 80, more preferably more than 120, as measured according to ASTM D2270.

There are no particular limitations regarding the kinematic viscosity of the base oil.

The amount of base oil present in a fully formulated lubricating oil composition will typically be the amount remaining to equal 100% after the remaining additives are accounted for. Generally, the base oil may be present in an amount in the range of from 50 to more than 99.99 wt. %, in an amount in the range of from 65 to 95 wt. %, in an amount in the range of from 70 to 90 wt. %, or in an amount in the range of from 75 to 88 wt. %, with respect to the total weight of the lubricating oil composition.

B. Defoaming Agent

In addition to the base oil, the lubricating oil compositions further comprise a defoaming agent comprising (i) a silicone oil and (ii) silica particulates.

The silicone oil is not generally limited and may include any silicone oil known in the art that does not adversely affect the lubricating properties of the resulting lubricating oil composition. Suitable silicone oils may include any liquid polymerized siloxane comprising one or more organic groups (“polyorganosiloxanes”). Examples of suitable silicone oils include, but are not limited to, polyalkylsiloxanes (e.g., polydimethylsiloxane), polyarylsiloxanes, polyalkoxysiloxanes, polyaryloxysiloxanes, fluorinated polysiloxanes (e.g., trifluoropropylmethylsilicone), combinations thereof, etc.

Polydimethylsiloxane is a known antifoam compound and may be produced, for example, by the hydrolysis of dimethyldihalosilane followed by condensation, or by the decomposition of dimethylcyclosiloxane followed by condensation. In certain embodiments, polydimethylsiloxane may be end blocked by the trimethylsilyl group or hydroxyl group, but is not so limited.

Generally, silicone oils suitable for use in the present invention have a kinematic viscosity at 25° C. of at least 0.5 mm²/s (cSt), or in a range of from 0.5 to 1,000,000 mm²/s (cSt), or in a range of from 10,000 to 600,000 mm²/s (cSt). Silicone oil may be present in a defoaming agent in an amount in the range of from 0.01 to more than 99 wt %, or in an amount in the range of from 1 to 10 wt %, based on the total weight of the defoaming agent. Further, the concentration of silicone oil present in the lubricating oil composition is typically in a range of from 0.1 to 500 ppm, from 1 to 100 ppm, or from 1 to 50 ppm.

The defoaming agent further comprises silica particulates. The silica particulates are not generally limited and may include any type of silica particulates that are conventionally employed in defoaming agents, provided that the silica particulates do not adversely affect the lubricating properties of the resulting lubricating oil composition. Examples of suitable silica particulates may include, but are not limited, colloidal silica, fumed silica, precipitated silica, silica aerogel, silica xerogel, silicas having surface organosilyl groups, chemically treated silica, hydrophobic silica, etc.

Suitable silica particulates may be produced by any known method, for example, a dry method such as the thermal decomposition of a silicon halide or the reaction of a substance containing silicic acid under heat, or a wet method such as the decomposition of a metal salt of silicic acid, e.g., sodium silicate, by an acid or the aerogel method. Various grades of silica particulates are commercially available from a variety of sources in a variety of particle size distributions. Although the size of silica particulates suitable for use in the defoaming agent is not particularly limited, the silica particulates generally may have a particle size of from about 1 nanometers (nm) to several microns. Preferably, the silica particulates may have a particle size of from about 1 to 1000 nm.

A silica aerogel is one kind of silica that may be employed. Briefly, such materials are prepared by displacing water from a silica hydrogel with a low boiling organic liquid such as ethyl alcohol, heating the treated gel in an autoclave to approximately the critical temperature of the organic liquid, and then releasing the vapors of the organic liquid from the autoclave whereby excessive shrinking or crushing of the cellular structure of the silica is avoided. The details of this technique are described in the literature and silica aerogels are commercially available.

Preferred silica particulates include “Aerosil® R208” and “Aerosil® R812” available from Evonik Industries, fumed silica available from Sigma-Aldrich Co. LLC and silica available from Chemicell GmbH.

Silica particulates may be present in a defoaming agent in an amount in the range of from 0.01 to more than 99 wt %, or in an amount in the range of from 0.1 to 10 wt %, based on the total weight of the defoaming agent. Further, the concentration of silica particulates present in the lubricating oil composition is typically in a range of from 0.1 to 500 ppm, from 1 to 100 ppm, or from 1 to 50 ppm.

Optionally, defoaming agents may further comprise a solvent, such as a paraffinic mineral oil, naphthenic mineral oil, petroleum naphtha, aromatics, toluene, xylene, benzene, hexane, heptane, octane, dodecane, kerosene, etc. and combinations thereof. Optionally, the silicone oil may be dispersed or dissolved in the solvent.

Optionally, the defoaming agent may further comprise other known defoamers such as, for example, a polyalkyl acrylate, an alcohol ethoxy/propoxylate, a fatty acid ethoxy/propoxylate, a sorbitan partial fatty acid ester, a siloxane resin, etc.

C. Other Additives

In addition to a base oil and a defoaming agent, the lubricating oil compositions may further comprise one or more additional additives to impart or enhance the desired properties of the fully formulated lubricating oil composition. These additives may be selected from many conventional types such as anti-oxidants, anti-wear additives, detergents, dispersants, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, extreme pressure additives, metal passivators and seal fix/seal compatibility agents.

Examples of suitable anti-oxidants include, but are not limited to, aminic antioxidants, phenolic antioxidants, and mixtures thereof. Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated α-naphthylamines.

Preferred aminic antioxidants include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine, 1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines such as phenothiazine and 3,7-dioctylphenothiazine.

Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.), “Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex. Hodogaya Kagaku Co.).

Examples of phenolic antioxidants which may be conveniently used include C₇-C₉ branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylenebis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol-formaldehyde condensates and p-t-butylphenol-acetaldehyde condensates.

Examples of suitable phenolic antioxidants include those which are commercially available under the following trade designations: “Irganox L-135” (ex. Ciba Specialty Chemicals Co.), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “Antage W-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi Kagaku Co.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Irganox L109” (ex. Ciba Specialty Chemicals Co.), “Tominox 917” (ex. Yoshitomi Seiyaku Co.), “Irganox L115” (ex. Ciba Specialty Chemicals Co.), “Sumilizer GA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.), “Irganox L101” (ex. Ciba Specialty Chemicals Co.), “Yoshinox 930” (ex. Yoshitomi Seiyaku Co.).

Optionally, antioxidants may be present in an amount in the range of from 0.1 to 5.0 wt. %, more preferably in an amount in the range of from 0.3 to 3.0 wt. %, and most preferably in an amount in the range of from 0.5 to 1.5 wt. %, based on the total weight of the lubricating oil composition.

Anti-wear additives that may be conveniently used include zinc-containing compounds such as zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, molybdenum-containing compounds, boron-containing compounds and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

Zinc dithiophosphate is a well-known additive in the art and may be conveniently represented by general formula II:

wherein R² to R⁵ may be the same or different and are each a primary alkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12 carbon atoms, a secondary alkyl group containing from 3 to 20 carbon atoms, preferably from 3 to 12 carbon atoms, an aryl group or an aryl group substituted with an alkyl group, said alkyl substituent containing from 1 to 20 carbon atoms preferably 3 to 18 carbon atoms.

Zinc dithiophosphate compounds in which R² to R⁵ are all different from each other can be used alone or in admixture with zinc dithiophosphate compounds in which R² to R⁵ are all the same.

Examples of suitable zinc dithiophosphates include those which are commercially available under the following trade designations: “Lz 1097”, “Lz 1395”, “Lz 677A”, “Lz 1095”, “Lz 1370”, “Lz 1371”, and “Lz 1373” (ex. Lubrizol Corporation); “OLOA 267”, “OLOA 269R”, “OLOA 260” and “OLOA 262” (ex. Chevron Oronite); and “HITEC 7197” and “HITEC 7169” (ex. Afton Chemical).

Examples of molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO 98/26030, sulphides of molybdenum and molybdenum dithiophosphate.

Boron-containing compounds that may be conveniently used include borate esters, borated fatty amines, borated epoxides, alkali metal (or mixed alkali metal or alkaline earth metal) borates and borated overbased metal salts.

Optionally, the lubricating oil compositions may comprise in the range of from 0.4 to 1.2 wt. % of an anti-wear additive, based on the total weight of the lubricating oil composition.

Typical detergents that may be used include one or more salicylate and/or phenate and/or sulphonate detergents. However, as metal organic and inorganic base salts which are used as detergents can contribute to the sulfated ash content of a lubricating oil composition, in a preferred embodiment, the amounts of such additives are minimized. Furthermore, in order to maintain a low sulphur level, salicylate detergents are preferred.

In order to maintain the total sulphated ash content of the lubricating oil composition at a level of preferably not greater than 2.0 wt. %, more preferably at a level of not greater than 1.0 wt. % and most preferably at a level of not greater than 0.8 wt. %, based on the total weight of the lubricating oil composition, the detergents are preferably used in amounts in the range of 0.05 to 20.0 wt. %, more preferably from 1.0 to 10.0 wt. % and most preferably in the range of from 2.0 to 5.0 wt. %, based on the total weight of the lubricating oil composition.

Furthermore, it is preferred that the detergents, independently, have a TBN (total base number) value in the range of from 10 to 500 mg·KOH/g, more preferably in the range of from 30 to 350 mg·KOH/g and most preferably in the range of from 50 to 300 mg·KOH/g, as measured by ISO 3771.

The lubricating oil composition may additionally comprise an ash-free dispersant which is preferably admixed in an amount in the range of from 5 to 15 wt. %, based on the total weight of the lubricating oil composition.

Examples of ash-free dispersants which may be used include the polyalkenyl succinimides and polyalkenyl succininic acid esters disclosed in Japanese Patent Nos. 1367796, 1667140, 1302811 and 1743435. Preferred dispersants include borated succinimides.

Examples of viscosity index improvers which may be conveniently used include the styrene-butadiene copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers. Such viscosity index improvers may be conveniently employed in an amount in the range of from 1 to 20 wt. %, based on the total weight of the lubricating oil composition.

Polymethacrylates may be conveniently employed as effective pour point depressants. For corrosion inhibitors, it is possible to use alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds.

Compounds which may be conveniently used as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

The lubricating oil compositions may be conveniently prepared in any manner, including using conventional formulation techniques. For example, the lubricating oil compositions may be prepared by admixing a base oil with a defoaming agent, or by admixing a base oil and the individual components of the defoaming agent, and, if desired, one or more additives.

The lubricating oil compositions may generally be used to lubricate any surface that is in relative movement to another surface. For example, the lubricating oils compositions may be used to lubricate a surface of a rotating or sliding member in a vehicle or industrial machine. The lubricating oils compositions may also be useful to lubricate a surface in an engine (e.g., an internal combustion engine), a gear mechanism, a speed-change gearbox, a bearing, a hydraulic apparatus, compression machinery, etc.

The disclosure herein further provides the use of a defoaming agent comprising a silicone oil and silica particulates for improving the foaming characteristics of a non-aqueous fluid (e.g., a lubricating oil, crude oil, etc). The foaming characteristics may be assessed using any suitable method. In general, such a method may involve measuring the foam stability and/or foaming tendency of a composition in accordance with ASTM D892. The methods and defoaming agents provided herein may be used to achieve any degree of improvement in the foaming characteristics of a non-aqueous fluid.

Additionally, the disclosure herein further provides the use of a defoaming agent comprising a silicone oil and silica particulates for improving the air release rate of a non-aqueous fluid (e.g., a lubricating oil, crude oil, etc). The air release rate may be assessed using any suitable method. In general, such a method may involve measuring the air release rate of a non-aqueous fluid in accordance with ASTM D892. The methods and defoaming agents provided herein may be used to achieve any degree of improvement in the air release rate of a non-aqueous fluid.

To facilitate a better understanding of the present invention, the following examples of certain aspects of some embodiments are given. In no way should the following examples be read to limit, or define, the entire scope of the invention.

Example 1

Foaming Characteristics

Six lubricating oil compositions were formulated as indicated in Table 1 (Formulations 1-6). All formulations were manufactured by blending using conventional mixing techniques.

Formulations 1-3 comprised a Fischer-Tropsch derived base oil having a kinematic viscosity at 40° C. (ASTM D445) of approx. 35 mm²/s (cSt) (“Base Oil A”). The Fischer-Tropsch derived base oil used may be conveniently manufactured by the process described in e.g. WO 02/070631, the teaching of which is hereby incorporated by reference.

Formulations 4-6 comprised a formulated oil that contained a mixture of Group I and Group III base oils and had a kinematic viscosity at 40° C. (ASTM D445) of approximately 33 mm²/s (cSt) (“Formulated Oil B”).

The silicone oil used was a commercially available polydimethylsiloxane from Dow Corning under the tradename “XIAMETER® PMX-200”.

The silica particulates were commercially available hydrophobic fumed silica from Evonik Industries under the tradename “Aerosil® R208”.

In order to evaluate the foaming tendency and the foam stability of Formulations 1-6, measurements were performed in accordance with ASTM D 892. The foam stability was zero for Formulations 1-6 and the measurements of foaming tendency are shown below in Table 1 (Formulations 1-3 were repeated once and the averages of D892 were shown).

TABLE 1 1 2 4 5 Component Comparative Comparative 3 Comparative Comparative 6 Silicone Oil — 50 50 — 50 50 (ppm) Silica — — 5 — — 5 Particulates (ppm) Base Oil A (wt 100% Remainder Remainder — — — %) Formulated Oil — — — 100% Remainder Remainder B (wt %) TEST RESULTS Kinematic 35 35 35 33 32 34 viscosity at 40° C.¹ [cSt] Seq I, 40 10 0 430 10 0 Tendency 0 mins², mL Seq II, 15 20 5 20 20 10 Tendency 0 mins², mL Seq III, 30 5 0 360 0 0 Tendency 0 mins², mL ¹According to ASTM D445 ²According to ASTM D892

As evident from the results shown in Table 1, the inclusion of a defoaming agent containing both silicone oil and silica particulates (as in Formulations 3 and 6) significantly reduces the foaming tendency.

Example 2

Air Entrainment Properties

Five lubricating oil compositions were formulated as indicated in Table 2 (Formulations 7-11). All formulations were manufactured by blending using conventional mixing techniques.

Formulations 7-11 contained a formulated oil based on a mixture of two Group IV base oils and had a kinematic viscosity at 40° C. (ASTM D445) of approximately 300 mm²/s (cSt) (“Formulated Oil C”).

The silicone oil used was a commercially available polydimethylsiloxane from Dow Corning under the tradename “XIAMETER® PMX-200”.

Silica particulates A were hydrophobic fumed silica commercially available from Evonik Industries under the tradename “Aerosil® R812”.

Silica particulates B were fumed silica commercially available from Sigma Aldrich under the tradename “S5505”.

The combination silicone oil/silica particulates product used was a 100% active silicone oil containing a suspension of finely powdered silica commercially available from Dow Corning under the tradename “Dow Corning® 2-3436”.

In order to evaluate the air release properties of Formulations 7-11, air release rate measurements were performed in accordance with ASTM D 3427. The results are shown below in Table 2.

Additionally, the foaming tendency and the foam stability of Formulations 8-11 were measured in accordance with ASTM D 892. The foam stability and the foaming tendency was zero for Formulations 8-11.

TABLE 2 7 8 Component Comparative Comparative 9 10 11 Silicone Oil (ppm) — 50 50 50 — Silica — — 5 — — Particulates A (ppm) Silica — — — 5 — Particulates B (ppm) Silicone Oil + — — — — 63 Silica Particulates (ppm) Formulated Oil C 100% Remainder Remainder Remainder Remainder (wt %) TEST RESULTS Kinematic 305 300 299 301 299 viscosity at 40° C.¹ [cSt] Air Release Time 11.5 18.1 14.1 13.4 12.8 at 75° C.², min ¹According to ASTM D 445 ²According to ASTM D 3427

As evident from the results shown in Table 2, a defoaming agent (which contains both silicone oil and silica particulates—as in Formulations 9-11) improves the air release rate of a lubricating oil composition, when compared to the use of silicone oil alone.

Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 

1. A lubricating oil composition comprising: a base oil; and a defoaming agent comprising (a) a silicone oil and (b) silica particulates.
 2. The lubricating oil composition of claim 1 wherein the silicone oil comprises polydimethylsiloxane.
 3. The lubricating oil composition of claim 1 wherein the silica particulates comprise hydrophobic fumed silica.
 4. The lubricating oil composition of claim 1 wherein the silicone oil comprises polydimethylsiloxane and the silica particulates comprise hydrophobic fumed silica.
 5. The lubricating oil composition of claim 1 wherein the silicone oil is present in the lubricating oil composition at a concentration of from about 0.1 to 500 ppm.
 6. The lubricating oil composition of claim 1 wherein the silica particulates are present in the lubricating oil composition at a concentration of from about 0.1 to 500 ppm.
 7. The lubricating oil composition of claim 1 wherein the silica particulates have a particle size of from about 1 to 1000 nm.
 8. The lubricating oil composition of claim 1 wherein the base oil is present in an amount of 50 to more than 99.99 wt. %, based on the total weight of the lubricating oil composition.
 9. A method comprising: applying a lubricating oil composition comprising a base oil; and a defoaming agent comprising (a) a silicone oil and (b) silica particulates to a surface in relative movement to another surface.
 10. The method of claim 9 wherein the surface is a surface of a rotating member or a sliding member in a vehicle or industrial machine.
 11. The method of claim 9 wherein the surface is in an engine, a gear mechanism, a speed-change gearbox, a bearing, a hydraulic apparatus or compression machinery.
 12. The method of claim 9 wherein the surface is in an internal combustion engine.
 13. A method of decreasing the foaming tendency or foaming stability of a non-aqueous fluid comprising: providing a non-aqueous fluid having a first foaming tendency or foaming stability as measured according to ASTM D892; and adding a defoaming agent comprising a silicone oil and silica to the non-aqueous fluid so as to reduce the first foaming tendency or foaming stability to a second foaming tendency or foaming stability.
 14. The method of claim 13 wherein the non-aqueous fluid is a lubricating oil.
 15. The method of claim 13 wherein the silicone oil comprises polydimethylsiloxane.
 16. The method of claim 13 wherein the silica particulates comprise hydrophobic fumed silica.
 17. A method of improving the air release rate of a non-aqueous fluid comprising: providing a non-aqueous fluid having a first air release rate as measured according to ASTM D3427; and adding a defoaming agent comprising a silicone oil and silica particulates to the non-aqueous fluid so as to increase the first air release rate to a second air release rate by reducing air release time.
 18. The method of claim 17 wherein the non-aqueous fluid is a lubricating oil.
 19. The method of claim 17 wherein the silicone oil comprises polydimethylsiloxane.
 20. The method of claim 17 wherein the silica particulates comprise hydrophobic fumed silica. 